There is good reason to believe the Church will never be destroyed. Jesus tells us very plainly that His words will never pass away, and that He will be where just two people gather in His name. But Matthew 16:18, a verse commonly cited to further support this claim, is actually misunderstood. This verse is actually not about Hell failing to overcome the Church, but about Hell failing to defend against it.
Consider this: A gate is not an offensive weapon. Soldiers do not carry gates around in holsters, nor do they use them to club their enemies. No, gates are built in front of passages to block either intruders from coming in, or prisoners from getting out. They are defensive structures.
The Gospel is a message that frees slaves from their bondage to sin and death. When you proclaim the Gospel, you are not under attack. We need to defend the Gospel, but not as if it is actually in danger. What Jesus is really telling us in Matthew 16:18 is that when the Church goes out to preach, Satan's forces cannot resist it. If God intends to save a person to whom you are preaching, they're going to get saved as surely as if a bomb was set on iron bars.
This should give us more encouragement than Christ promising His Church will never disappear. It's one thing to know there will always be Christians, it's another thing to know our preaching will be effective. Our mouths are lethal weapons. We can drop demons like a tonne of bricks. We can shred lies like curtains. The gates that trap people in sin, we can knock down like skittles. So what are you doing hiding in your church? Step outside, find a lost soul, tell them about the hope you have. With God on your side, or more accurately with you on His, the mission will succeed.